Naval forces from the US, the Philippines, Japan, New Zealand, and Australia conducted joint drills in the disputed South China Sea, amid growing regional tensions, official and local media reported Saturday.

The exercises, known as the 4th Multilateral Maritime Cooperative Activity, took place within an unspecified area of the Philippines' exclusive economic zone in the South China Sea, according to a statement from the US Indo-Pacific Command.

"The U.S., along with our allies and partners, uphold the right to freedom of navigation and overflight, other lawful uses of the sea and international airspace, as well as respect for maritime rights under international law," the US command said.

Earlier this week, Japan’s Maritime Self-Defense Force transited the Taiwan Strait for the first time to join the drills, a move that angered China. Beijing lodged a formal protest with Japan on Thursday.

"The Taiwan question concerns China's sovereignty and territorial integrity, and is the political foundation of China-Japan relations," said Chinese Foreign Ministry spokesman Lin Jian. "It is a red line that must not be crossed."

Meanwhile, China's People’s Liberation Army (PLA) Southern Theater Command launched its own navy and air force drills near Huangyan Dao, also known as Scarborough Shoal, in the South China Sea.

In a statement, the Chinese military criticized the US and its allies, accusing outside countries of "stirring up trouble" and causing instability in the region, according to state-run Xinhua News. The PLA reaffirmed China’s "indisputable sovereignty" over Huangyan Dao and its surrounding waters, vowing to remain on high alert to defend its national interests.

The joint exercises come just a month after the Philippines, U.S., Australia, and Canada held similar sea and air drills in the South China Sea, at the same time China was conducting its own military exercises in the contested waters.

The Philippines, bolstering its defense ties with key U.S. allies, also conducted its first joint maritime drill with Japan in the region earlier this year.

Tensions over the South China Sea have been escalating as the Philippines seeks stronger military cooperation with the U.S. and its allies in response to China’s growing assertiveness in the area.